In hard disk drives, data is written to and read from magnetic recording media, herein called disks, utilizing magnetoresistive (MR) transducers commonly referred to as MR heads. Typically, one or more disks having a thin film of magnetic material coated thereon are rotatably mounted on a spindle. An MR head mounted on an actuator arm is positioned in close proximity to the disk surface to write data to and read data from the disk surface.
During operation of the disk drive, the actuator arm moves the MR head to the desired radial position on the surface of the rotating disk where the MR head electromagnetically writes data to the disk and senses magnetic field signal changes to read data from the disk. Usually, the MR head is integrally mounted in a carrier or support referred to as a slider. The slider generally serves to mechanically support the MR head and any electrical connections between the MR head and the disk drive. The slider is aerodynamically shaped, which allows it to fly over and maintain a uniform distance from the surface of the rotating disk.
Typically, an MR head includes an MR read element to read recorded data from the disk and an inductive write element to write the data to the disk. The read element includes a thin layer of magnetoresistive sensor stripe sandwiched between two magnetic shields that are electrically connected together but are otherwise isolated. The shields are constructed so that one is just upstream of the sensor stripe and one is just downstream of the sensor stripe. A constant current is passed through the sensor stripe, and the resistance of the magnetoresistive stripe varies in response to a previously recorded magnetic pattern on the disk. In this way, a corresponding varying voltage is detected across the sensor stripe. The magnetic shields help the sensor stripe to focus on a narrow region of the magnetic medium, hence improving the spatial resolution of the read head.
Earlier MR sensors operated on the basis of the anisotropic magnetoresistive (AMR) effect in which a component of the read element resistance varied as the square of the cosine of the angle between the magnetization and the direction of sense current flowing through the read element. In this manner, because the magnetic field of the recording media would effect the magnetization direction within the read element, the change in resistance could be monitored to determine the type of external magnetic field applied by the magnetic recording medium. Most current disk drive products utilize a different, more pronounced magnetoresistive effect known as the GMR or spin valve effect. This effect utilizes a layered magnetic sensor that also has a change in resistance based on the application of an external magnetic field.
Competitive pressures drive the need to increase areal density in each new product generation. Increased areal density for longitudinal magnetic recording is facilitated by smaller magnetic spacing between the read/write transducer and the recording media, because of the higher signal strength and resolution that lower spacing provides. Conventionally, lower magnetic spacing is achieved by reducing the dimension of every material intervening between the transducer and media, including media carbon overcoat, head overcoat, and air bearing. The pressure for lower magnetic spacing has been especially demanding on air bearing technology to produce large populations of heads with narrow distributions in flying attitude and little variance in fly height when accessing different data tracks.
One phenomenon that affects how closely heads can be flown to the disk is write pole tip protrusion (WPTP). This is when the portion of the ABS in the region of the write transducer protrudes toward the disk due to the thermal expansion of materials in the head due to the higher temperatures experienced by those materials during writing operations. Because of this protrusion, prior art heads needed to be spaced apart from the disk by at least this amount so that when WPTP occurred there would be no contact between the head and the disk.
It is against this background and a desire to improve on the prior art that the present invention has been developed.